When I activate the 4wd in my 1996 GMC Yukon, I notice a clunk coming from right under the drivers seat about every 100 ft. It becomes worse when going uphill, it sometimes doesn't even happen on flat ground. Prior to my ownership of the vehicle the diff fluids were changed regularly and 4wd was rarely engaged. Transfer case was rebuilt about 70k miles ago.
Could it be the U-Joints on the front drive shaft or is it for sure the differential? Is there anything else it could be?
Thanks for the initial response. To clarify, I only engage 4wd on dirt or snow and the clunking doesn't happen when I turn, just when I'm moving straight ahead.
It should clunk if you are driving on asphalt or any surface not allowing wheel slip. Especially when turning. If you’re in dirt or gravel it still may happen occasionally if the wheel isn’t allowed to slip. If that isn’t it you could have a joint in the front having issues. Also when not used refularly the wheel hib lockup can stick, not engaging all the way. I wouldn’t use it anymore until you have a mechanic check it out. If something isn’t engaging 100% you can stripout gears.
This is a symptom for the front drive shaft u joints and possibly the double Cardan joint being worn out. Front shaft needs a rebuild.
